Evaluation of Transparent Insulation Materials in Flat Plate Collectors

Technical Report · Thu Dec 01 04:00:00 EST 1994

DOI:https://doi.org/10.2172/1577037· OSTI ID:1577037

Emrich, Carol ^[1]; Coffman, Roy ^[1]

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1. Florida Solar Energy Center, Cape Canaveral, FL (United States)

Polycarbonate rectangular honeycomb and acrylic capillary honeycomb, two types of transparent insulation material, were tested in flat-plate collectors. The honeycomb was inserted between the cover plate and the absorber, leaving a 1-cm air gap above the absorber to decouple radiative and conductive heat-transfer modes. Four 4 by 8 ft. collectors with selective black chrome absorbers were evaluated side by side using ASHRAE Standard 93-1986. They differed in thickness and type of material as follows: 1) no insulation material, 2) 1 in. of polycarbonate, 3) 4-in. of polycarbonate, and 4) 4 in. of acrylic honeycomb. Another set of tests was completed using absorbers coated with moderately selective black paint, and a third set with flat-black paint. A collector containing a selective chrome absorber and 4 in. of acrylic honeycomb achieved the best thermal performance. The amount of improvement in thermal performance was greatest when transparent insulation material was added to collectors with flat-black absorbers, and it decreased as absorber selectivity increased. Since small-cell honeycomb improves thermal performance by suppressing both convective and radiative transfer, combination with selective coatings is partially redundant because they are poor emitters. Also, the unacceptably low melting temperature of these materials preclude them from withstanding even a wet stagnation, thereby rendering this application impractical.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Florida Solar Energy Center, Cape Canaveral, FL (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 1577037
• Report Number(s): SAND--94-2552; 681674
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
CSP
Concentrating Solar Power